CT and MR imaging of malignant germ cell tumor of the undescended testis.

Preoperative localization of the impalpable undescended testis is necessary to facilitate proper surgical planning. There is an increased incidence of malignant change in the undescended testis; demonstration of malignancy before surgery will significantly alter the treatment. We describe the computed tomographic (CT) and magnetic resonance (MR) findings in 2 patients with malignant change in an intraabdominal testis. The CT scan revealed lesions with areas of low density, 1 of which had focal calcifications; MR revealed lesions of predominantly low or intermediate signal intensity on both long and short TR/TE images, with some areas of very high signal on both sequences. After initial management with chemotherapy, the residual tumor was surgically resected. In neither instance was residual normal testis demonstrated. Both CT and MR are ideal methods of examining malignant transformation of the undescended testis, because of their ability to characterize the internal structure of the organ and, in the case of MR, its capacity for multiplanar imaging. They are almost of equal value except for the ability of CT to identify calcification and of MR to diagnose hemorrhage.